Radio interferometry at millimetre and sub-millimetrewavelengths
Bojan Nikolic1 & Frederic Gueth2
1 Cavendish Laboratory/Kavli Institute for CosmologyUniversity of Cambridge
2 Institut de Radioastronomie MillimetriqueGrenoble
ERIS 2009Oxford, September 2009
Rev 33
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 1 / 62
Introduction
Outline
1 IntroductionScientific differences from the cm/m-wave bandObservational differences from the cm/w-wave bandScience examples
2 Current and forthcoming mm and sub-mm arrays
3 Atmospheric effects/other calibration uncertaintiesPhase fluctuationsAmplitude calibration uncertainties
4 Offline calibration/imaging
5 Summary
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 2 / 62
Introduction
MM/sub-mm bands (ALMA site, 1mm water)The numbers shown are the ALMA band designations (+ band 1 at 30-45 GHz)
Band 2
Band 3 Band 4
Band 5
Band 6
Band 7
Band 8 Band 9
Band 10
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0.2
0.4
0.6
0.8
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T xT x
100 200 500 1000
ν (GHz)ν (GHz)B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 3 / 62
Introduction Scientific differences from the cm/m-wave band
Some of the fundamental science from other bands
Most science targets ‘cool’ and close to thermal equilibriumRotational lines of molecules, dust continuum, atomic carbon
Emission mechanisms are energetically significant for starformation both on local and galaxy-wide scalesRelatively low opacity except in the strongest molecular linesStrong positive cosmological ‘K-correction’
Continuum from star-forming galaxies does not dim from z = 1 toz ∼ 8
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 4 / 62
Introduction Scientific differences from the cm/m-wave band
Some of the fundamental science from other bands
Most science targets ‘cool’ and close to thermal equilibriumRotational lines of molecules, dust continuum, atomic carbon
Emission mechanisms are energetically significant for starformation both on local and galaxy-wide scalesRelatively low opacity except in the strongest molecular linesStrong positive cosmological ‘K-correction’
Continuum from star-forming galaxies does not dim from z = 1 toz ∼ 8
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 4 / 62
Introduction Scientific differences from the cm/m-wave band
CO emission line ladder in Milky WayFixsen et al. (1999)
Lines show models S ∝ ν4 exp[−E/kT ]
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 5 / 62
Introduction Scientific differences from the cm/m-wave band
Some of the fundamental science from other bands
Most science targets ‘cool’ and close to thermal equilibriumRotational lines of molecules, dust continuum, atomic carbon
Emission mechanisms are energetically significant for starformation both on local and galaxy-wide scalesRelatively low opacity except in the strongest molecular linesStrong positive cosmological ‘K-correction’
Continuum from star-forming galaxies does not dim from z = 1 toz ∼ 8
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 6 / 62
Introduction Scientific differences from the cm/m-wave band
Spectral energy distribution of galaxiesLagache et al. (2005)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 7 / 62
Introduction Scientific differences from the cm/m-wave band
Some of the fundamental science from other bands
Most science targets ‘cool’ and close to thermal equilibriumRotational lines of molecules, dust continuum, atomic carbon
Emission mechanisms are energetically significant for starformation both on local and galaxy-wide scalesRelatively low opacity except in the strongest molecular linesStrong positive cosmological ‘K-correction’
Continuum from star-forming galaxies does not dim from z = 1 toz ∼ 8
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 8 / 62
Introduction Scientific differences from the cm/m-wave band
Dust extinction model: UV to near-IRDraine (2003)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 9 / 62
Introduction Scientific differences from the cm/m-wave band
Dust extinction model: near-IR to mm-waveDraine (2003)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 10 / 62
Introduction Scientific differences from the cm/m-wave band
Some of the fundamental science from other bands
Most science targets ‘cool’ and close to thermal equilibriumRotational lines of molecules, dust continuum, atomic carbon
Emission mechanisms are energetically significant for starformation both on local and galaxy-wide scalesRelatively low opacity except in the strongest molecular linesStrong positive cosmological ‘K-correction’
Continuum from star-forming galaxies does not dim from z = 1 toz ∼ 8
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 11 / 62
Introduction Scientific differences from the cm/m-wave band
Positive cosmological K-correctionLagache et al. (2005)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 12 / 62
Introduction Observational differences from the cm/w-wave band
Outline
1 IntroductionScientific differences from the cm/m-wave bandObservational differences from the cm/w-wave bandScience examples
2 Current and forthcoming mm and sub-mm arrays
3 Atmospheric effects/other calibration uncertaintiesPhase fluctuationsAmplitude calibration uncertainties
4 Offline calibration/imaging
5 Summary
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 13 / 62
Introduction Observational differences from the cm/w-wave band
Fundamental observational differences from cm/mwave
Small field of viewFiner resolution (yet to be fully realised)High cost per element of the arrayLack of zero-spacing (‘total-power’) and short-spacing informationSky has a small dynamic range, low surface brightness of typicalsourcesMechanical effects on antennas are importantTroposphere gets seriously in the way, ionosphere not importantLarge absolute – but small fractional – bandwidthsCurrent arrays do not have good instantaneous uv -coverage
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 14 / 62
Introduction Observational differences from the cm/w-wave band
Contrast vs single dish
Single dish continuum surveys are confusion limited –interferometry essential for really deep surveysMuch easier to integrate down:
Atmospheric brightness fluctuations are rejectedStanding waves are rejectedGain fluctuations of the receivers less important
Better astrometryGood surface brightness sensitivity is expensive
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 15 / 62
Introduction Science examples
Outline
1 IntroductionScientific differences from the cm/m-wave bandObservational differences from the cm/w-wave bandScience examples
2 Current and forthcoming mm and sub-mm arrays
3 Atmospheric effects/other calibration uncertaintiesPhase fluctuationsAmplitude calibration uncertainties
4 Offline calibration/imaging
5 Summary
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 16 / 62
Introduction Science examples
Identifying the sub-mm galaxies (LH850.02)Younger et al. (2009)
Deep R-band SUBARU image with SCUBA centroid (dashed) and 2-σposition ellipsoid (dotted)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 17 / 62
Introduction Science examples
Identifying the sub-mm galaxies (LH850.02)Younger et al. (2009), SMA 890 µm and R-band SUBARU
SMA (colour scale) SUBARU R-band image+ SCUBA beam (dashed) + SMA position (yellow circle)+ SCUBA position (dotted)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 18 / 62
Introduction Science examples
Identifying the sub-mm galaxies (LH850.02)Younger et al. (2009), Spitzer and VLA
IRAC 3.6µm VLA 1.4 GHz+ SMA position (yellow circle) + SMA position (yellow circle)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 19 / 62
Introduction Science examples
Imaging of CO in a z = 6.42 quasar hostRiechers et al. (2009) [detection of C I also presented in the paper]
CO J 7→ 6 emission (contours) CO J 7→ 6 spectrumCO J 3→ 2 (colour scale)
PdB λ ∼ 3 mm observations
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 20 / 62
Introduction Science examples
Resolving the [C II] emission in the z = 6.42 hostWalter et al. (2009)
Red− and blue−shifted [CII][CII] emissionContinuum emission
CO(3−2)
[C II] rest-frame wavelength is 158µmThese PdB observations at λ ∼ 1.1 mm
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 21 / 62
Current and forthcoming mm and sub-mm arrays
Outline
1 IntroductionScientific differences from the cm/m-wave bandObservational differences from the cm/w-wave bandScience examples
2 Current and forthcoming mm and sub-mm arrays
3 Atmospheric effects/other calibration uncertaintiesPhase fluctuationsAmplitude calibration uncertainties
4 Offline calibration/imaging
5 Summary
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 22 / 62
Current and forthcoming mm and sub-mm arrays
Existing (sub-)mm arrays
IRAM PdB: 6× 15-m antennasFunded by France, Germany and SpainOpen to all EU countries via RadioNet TNA
CARMA: 6× 10.4-m + 8× 6.1-m + 8×3.5-m antennasSMA: 8× 6-m antennasNobeyama Millimetre Array: 6× 10-m antennaSpecialised array for cosmic background: CBI, VSA, DASI, ...
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 23 / 62
Current and forthcoming mm and sub-mm arrays
IRAM PdB array
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 24 / 62
Current and forthcoming mm and sub-mm arrays
IRAM PdB array – max baseline ∼ 800 m
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 24 / 62
Current and forthcoming mm and sub-mm arrays
Current: Sub-Millimetre Array (SMA)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 25 / 62
Current and forthcoming mm and sub-mm arrays
Near Future: ALMA50×12-m+ 12×7-m antennas, currently being commissioned
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 26 / 62
Atmospheric effects/other calibration uncertainties
Outline
1 IntroductionScientific differences from the cm/m-wave bandObservational differences from the cm/w-wave bandScience examples
2 Current and forthcoming mm and sub-mm arrays
3 Atmospheric effects/other calibration uncertaintiesPhase fluctuationsAmplitude calibration uncertainties
4 Offline calibration/imaging
5 Summary
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 27 / 62
Atmospheric effects/other calibration uncertainties
Troposphere
(Sub-)mm radiation ispredominantly affected by thetroposphere→ (Sub-)mm telescopes aresited at high elevations(Mauna Kea, Chajnator, SP),airborne observatories(SOFIA) or spaceLittle effect on polarisation
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 28 / 62
Atmospheric effects/other calibration uncertainties
Two molecular species most significant: H2O and O2
Atmospheric transmission broken down into contributions from: H2O (blue)and O2 (red), and total (black)
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B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 29 / 62
Atmospheric effects/other calibration uncertainties
H2O is not well mixed
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 30 / 62
Atmospheric effects/other calibration uncertainties
Atmospheric transparencyModel of atmospheric conditions at summit of Mauna Kea
Sky Transparency Sky brightness (in K)
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Loss of astronomical signal + Additional noise
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 31 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
Atmospheric path fluctuations
Refractive index n 6= 1:
n − 1 ≈10−6[α
Pd
T+ β
Pw
T+ γ
Pw
T 2
]
Pw : Partial pressure of the water vapourT : Temperature of the water vapourFurthermore, the refractive index is a function of frequency (i.e.,the atmosphere is dispersive), especially at sub-mm frequenciesand close to the edges of the bandsHorizontal and line of sight variation in atmospheric propertieslead to phase errors and phase fluctuations
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 32 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
Example of path fluctuationsSMA, Mauna Kea, Hawaii
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Measured pathwhile observinga quasar200 m baselineAbout 3.5 mmline-of-sightwaterσφ = 207µm.
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 33 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
Correlation between baseline length and fluctuation
The phase fluctuation measured at 22 GHz at the VLA by observing a quasarfor about thirty minutes. Correlations along one arm of the VLA only shown.
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Pha
seflu
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baseline length (m)baseline length (m)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 34 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
Effect of uncorrected phase errorsFrom simulations in ALMA Memo # 582
Point-source sensitivity Gaussian beam size
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‘Decorrelation’ Limit on possible resolution
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 35 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
Effect of uncorrected phase errors on ‘snapshots’From simulations in ALMA Memo # 582
Positional error Fractional flux error
0.001
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√ 〈∆P
2〉(
arcs
ecs)
√ 〈∆P
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0.01 0.02 0.05 0.1 0.2 0.5 1 2 5
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Astrometric errors Flux calibration errors
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 36 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
Correcting the phase fluctuations
(Wait for stable weather)The magnitude of fluctuations can vary by a factor of five
Switch to a quasar and measure the phase, apply to scienceEssentially the same as normal phase calibrationTo be effective v∆t
2 < BCorrection with Water Vapour Radiometers (WVRs)
Measure water vapour along line of sight of each antennaInfer the path fluctuation on one second timescaleCorrect for the resulting phase errors
Self-calibrationSmall field of view, small dynamic range of sky→ only possible inspecialised projectsExample: quasar absorption lines
‘Paired-antenna’ technique: Dedicated antennas continuouslymonitoring a quasar
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 37 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
IRAM PdB 22 GHz WVRs
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 38 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
ALMA 183 GHz WVRsBlue rectangles are the WVR filters
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T b(K
)T b
(K)
175 177.5 180 182.5 185 187.5 190
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B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 39 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
How WVR phase correction worksALMA WVRs + SMA: Channel 3 data from two telescopes
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175
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T B,3
(K)
T B,3
(K)
16.75 17 17.25 17.5 17.75 18
t (hours UT)t (hours UT)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 40 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
How WVR phase correction worksALMA WVRs + SMA: Channel 3 difference & phase
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L(µ
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L(µ
m)
16.75 17 17.25 17.5 17.75 18
t (hours UT)t (hours UT)
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−6
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∆TB
,3(K
)∆T
B,3
(K)
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 41 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
How WVR phase correction worksALMA WVRs + SMA: Channel 3 phase prediction and residual
Uncorrected path fluctuation: 157µm RMS
Estimated Optimum
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p(µ
m)
p(µ
m)
16.8 17 17.2 17.4 17.6 17.8
t (hours UT)t (hours UT)
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∆p(µ
m)
∆p(µ
m)
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p(µ
m)
p(µ
m)
16.8 17 17.2 17.4 17.6 17.8
t (hours UT)t (hours UT)
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∆p(µ
m)
∆p(µ
m)
Residual RMS 74µm Residual RMS 71µm
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 42 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
WVR correction in practice at the PdB
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 43 / 62
Atmospheric effects/other calibration uncertainties Phase fluctuations
WVR correction in practice at the PdBExample of point source observation
Turbulent conditions, 4.4 mm precipitable water vapour, long baselinesNo WVR correction With WVR correction
×2.5 improvement in signal/noise
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 44 / 62
Atmospheric effects/other calibration uncertainties Amplitude calibration uncertainties
Amplitude calibration uncertainties
Fundamental uncertainties1 Atmospheric transparency varies with time and with frequency2 Receiver gain is variable3 Antenna gain is difficult to measure and sometimes variable
Difficult to inject a signal of known strengthQuasars are highly variable at (sub-)mm wavelengthsSolar system bodies (e.g., Mars, Neptune) also variable, but canbe modelled
Accurate models for the radiometric brightness are requiredMay be resolved, especially at sub-mm wavelengths
→ A calibration chain is required
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 45 / 62
Atmospheric effects/other calibration uncertainties Amplitude calibration uncertainties
Flux calibration chain
Build reasonably stable receiver systemsCalibrate receiver gain using hot and ambient load
every ∼ few to tens of minutesCalibrate atmospheric absorption through a combination of:
Tipping scans (once ∼ 1 hour)Atmospheric models and WVRs (could go as short as ∼ 1 second)Total power atmospheric emission[Quasar observations (once ∼ 3 mins)]
Calibrate antenna gains using primary calibration standardsonce per session – once a yearat short wavelengths only planets may be suitable
Calibrate antenna primary beam shape through directinterferometric measurement
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 46 / 62
Offline calibration/imaging
Outline
1 IntroductionScientific differences from the cm/m-wave bandObservational differences from the cm/w-wave bandScience examples
2 Current and forthcoming mm and sub-mm arrays
3 Atmospheric effects/other calibration uncertaintiesPhase fluctuationsAmplitude calibration uncertainties
4 Offline calibration/imaging
5 Summary
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 47 / 62
Offline calibration/imaging
Bandpass calibration
Principle:Frequency-dependence of gain is independent of time
Calibration steps:Observe a strong quasar at beginning of each session(Need high SNR since can not combine the channels)Fit (complex) gain vs frequency
If SNR is high solve for each channel individuallyOtherwise fit a smooth function of frequency
Apply this bandpass solution to all other data in the session
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 48 / 62
Offline calibration/imaging
Bandpass calibration: PdB example – amplitude
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 49 / 62
Offline calibration/imaging
Bandpass calibration: PdB example – phase
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 49 / 62
Offline calibration/imaging
Bandpass calibration: SMA Data + CASAAmplitude – two out of 24 spectral windows shown
Antennas 1&2 Antennas 1&3 Antennas 1&4
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Channel Velocity (km/s)
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B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 50 / 62
Offline calibration/imaging
Bandpass calibration: SMA Data + CASAPhase – two out of 24 spectral windows shown
Antennas 1&2 Antennas 1&3 Antennas 1&4
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Channel Velocity (km/s)
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Antennas 1&5 Antennas 1&6
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B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 51 / 62
Offline calibration/imaging
Phase calibration
Principles:Observed phase of a point source at phase centre should be zeroThe phase response of telescope will change very little for smallangular changes on the skyMost causes of errors are antenna-based and independent ofbaseline
Calibrations steps:Observe quasars every 10 seconds to 20 minutesFit (complex) gain vs time to estimate phase variation
If SNR is low and you think phase should be varying slowly, fitsmooth functionsIf SNR is high or there are jumps, use linear interpolation
Apply phase solution to science data
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 52 / 62
Offline calibration/imaging
Phase calibration: PdB Example – smooth phasevariation
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 53 / 62
Offline calibration/imaging
Phase calibration: PdB Example – jump ignored bysmooth fit
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 53 / 62
Offline calibration/imaging
Phase calibration: PdB Example – use higher orderfunction
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 53 / 62
Offline calibration/imaging
Phase transfer
Principles:Low frequency receivers are more sensitive, atmosphere moretransparent, telescopes more efficientQuasar spectra often roughly ∝ ν−0.7
→ easier to make phase calibration observations at lowerfrequency
Calibration steps:Observe phase calibration targets at 3 mmScale phase solutions to science bands and apply to data
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 54 / 62
Offline calibration/imaging
Phase transfer: PdB Example
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 55 / 62
Offline calibration/imaging
Phase transfer: PdB Example – with transferredcorrection
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 55 / 62
Offline calibration/imaging
Amplitude/Flux calibration
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 56 / 62
Offline calibration/imaging
Amplitude/Flux calibration
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 56 / 62
Offline calibration/imaging
Amplitude/Flux calibration
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 56 / 62
Offline calibration/imaging
Imaging
Imaging generally tractable with established techniquesAdding short/zero-spacing one important challenge but nowalmost routine in some systems
Comparison
(sub-)mm observations vs cm/m Science Imaging
Resolution (∼ λ/B) (current arrays) § ©Field of View (∼ λ/D) § ©Few pixels in image (∼ B/D) (current arrays) § ©Many spectral channels © §Low signal-to-noise § ©
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 57 / 62
Offline calibration/imaging
Short-spacing informationBelloche & Andre (2004), Class 0 proto-star observations
PdB only – dashed circle is the primary beam
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 58 / 62
Offline calibration/imaging
Short-spacing informationBelloche & Andre (2004), Class 0 proto-star observations
PdB + short spacing from IRAM 30-m
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 58 / 62
Summary
Outline
1 IntroductionScientific differences from the cm/m-wave bandObservational differences from the cm/w-wave bandScience examples
2 Current and forthcoming mm and sub-mm arrays
3 Atmospheric effects/other calibration uncertaintiesPhase fluctuationsAmplitude calibration uncertainties
4 Offline calibration/imaging
5 Summary
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 59 / 62
Summary
Summary
The physics of (sub-)mm emission means observing it allowsunique scienceInterferometers open the possibility of high-resolution and deepobservationsTroposphere has a big effect on (sub-)mm radiation butcombination of excellent sites and new techniques can/will resolvemost of theseMany of the techniques are the same as traditional cm-waveinterferometryIRAM mm-interferometry summer schools: next year
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 60 / 62
Summary
Resources on the web
Brogan et al: CASA training pages:http://casa.nrao.edu/casatraining.shtml
IRAM MM-Interferometry Summer School:http://www.iram.fr/IRAMFR/IS/presentations.html
Schilke, P: “ Interferometric Calibration & Imaging” http://www.astro.uni-bonn.de/˜bertoldi/wiki/RadioInterferometry
B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 61 / 62
Summary
References
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B. Nikolic & F. Gueth (Cambridge/IRAM) (Sub-)mm Wave Interferometry ERIS 2009 62 / 62